Fault Calculations - Typical Equipment Parameters 

By on

A frequent problem in fault calculations is the obtaining of equipment parameters. While it is always preferable to use the actual parameters of the equipment, sometimes these are not available. In this instance it is necessary to resort to the use of typical parameters.

This note is intended to become a collection of typical parameters. If there is something missing or needs adding, please leave a comment in the discussion.

HV Network Impedance

Impedance of HV network referred to LV side of transformer

Psc Uo (V) Ra (mΩ) Xa (mΩ)
250 MVA 420 0.106 0.71
500 MVA 420 0.053 0.353

Low Voltage Power Transformers

Transformer Short Circuit Impedance

Typical values short circuit impedance, USC for different kVA ratings (HV winding < 20 kV)

  Type of Transformer
transformer rating oil-immersed cast-resin
50 to 630 4% 6%
800 to 2500 6% 6%

Transformer Impedance (400 V)

Resistance, reactance and impedance for typical transformers (HV winding <20 kV)

transformer rated power (kVA) 50 100 160 250 315 400 500 630 800 1000 1250 1600 2000 2500
oil-immersed Usc % 4 4 4 4 4 4 4 4 6 6 6 6 6 6
  Rtr 95.3 37.9 16.2 9.2 6.9 5.1 3.9 2.9 2.9 2.3 1.8 1.4 1.1 0.9
  Xtr 104.1 59.5 41.0 26.7 21.3 16.9 13.6 10.8 12.9 10.3 8.3 6.5 5.2 4.1
  Ztr 141.1 70.5 44.1 28.2 22.4 17.7 14.1 11.2 13.2 10.6 8.5 6.6 5.3 4.2
cast-resin Usc % 6 6 6 6 6 6 6 6 6 6 6 6 6 6
  Rtr   33.5 18.6 10.7 8.2 6.1 4.6 3.5 2.6 1.9 1.5 1.1 0.8 0.6
  Xtr   100.4 63.5 41.0 32.6 25.8 20.7 16.4 13.0 10.4 8.3 6.5 5.2 4.2
  Ztr   105.8 66.2 42.4 33.6 26.5 21.2 16.8 13.3 10.6 8.4 6.6 5.3 4.2

 

Synchronous Machines

Performance Under Fault Conditions

Sub-transient emf:  myElectrical Equation

Transient emf:  myElectrical Equation 

Synchronous emf:  myElectrical Equation
Fault current: myElectrical Equation

Typical Machine Reactances

Typical Machine Reactances (& Time Constants

  Cylindrical Rotor
Turbine Generators

Salient Pole Generators
  Salient Pole
Synchronous
Condensers

Conventional
Direct
Cooled

4 Pole

Multi-Pole
Synchronous
Direct axis Xd pu 1.6-2.0 0.8-1.0 2.0-2.3 2.1-2.4 1.3-2.1 1.3-1.5
Quadrature axis Xq pu 1.0-1.25 0.5-0.65 1.95-2.1 1.95-2.25 0.6-1.2 0.8-1.0
Transient
Reactance  Xd' pu 0.3-0.5 0.2-0.35 0.18-0.25 0.27-0.30 0.15-0.35 0.4-0.5
Short circuit τd' s 1.5-2.5 1.0-2.0 0.75-1.0 0.75-1.0 0.8-1.2 0.8-1.2
Open circuit τdo' s 5-10 3-7 4-8 6-9.5 4-8 3-7
Sub-transient
Direct axis Xd'' pu 0.2-0.4 0.12-0.25 0.11-0.13 0.19-0.23 0.1-0.25 0.2-0.35
Quadrature axis Xq'' pu 0.25-0.6 0.15-0.45 0.11-0.13 0.19-0.23 0.14-0.35 0.2-0.35
Short circuit - direct axis τd' s 0.04-0.09 0.05-0.10 0.015-0.025 0.02-0.03 0.02-0.04 0.02-0.07
Open circuit - direct axis τd'' s 0.07-0.11 0.08-0.25 0.015-0.025 0.02-0.03 0.04-0.07 0.02-0.07
Short circuit - quadrature axis τq'' s 0.04-0.6 0.05-0.6 0.015-0.025 0.02-0.03 0.10-0.15 0.02-0.07
Open circuit - quadrature axis τq0'' s 0.1-1.2 0.2-0.9 0.015-0.025 0.02-0.03 0.3-0.7 0.1-0.2
Other Reactances
Negative sequence X-ve pu 0.25-0.5 0.14-0.35 0.11-0.13 0.19-0.23 0.12-0.3 0.2-0.35
Zero sequence  Xo pu 0.12-0.16 0.06-0.10 0.05-0.075 0.11-0.16 0.03-0.10 0.1-0.2

Cables

myElectrical Equation
myElectrical Equation

where:

d = distance between centre
r = geometric mean radius
a = cross sectional area (mm)

TypicalEquipmentCables



Steven McFadyen's avatar Steven McFadyen

Steven has over twenty five years experience working on some of the largest construction projects. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. About the author

myElectrical Engineering

comments powered by Disqus



How Electrical Circuits Work

If you have no idea how electrical circuits work, or what people mean then they talk about volts and amps, hopefully I can shed a bit light.  I’m intending...

Understanding Circuit Breaker Markings

IEC 60947 is the circuit breaker standard and covers the marking of breakers in detail. Any manufacturer following this standard should comply with the...

Introduction to Traction Substations

Following on from my post on railway electrification voltages, I thought an introduction to traction substations would be a good idea. Traction substations...

Capacitor Theory

Capacitors are widely used in electrical engineering for functions such as energy storage, power factor correction, voltage compensation and many others...

Periodic Electrical Installation Inspection – What to Inspect?

This is the second post in a series of two on periodic electrical inspections. In the first post, I discussed how often inspections should be carried out...

Wiki Depreciation

We have had the Wiki with us for a long time now, but at last I have decided to say bye bye – more details on why below.

Alternating Current Circuits

Alternating current (a.c.) is the backbone of modern electrical power distribution. In this article I’ll be pulling some of the more important concepts...

What happened to the cable notes?

If you are wondering what happened to our cable notes, the short answer is that we have moved them to myCableEngineering.com.  The "Knowledge Base" at...

Aluminium Windings - Dry Type Transformers

The other day I was talking to a colleague who is a building services consultant.  Despite regularly specifying dry-type/cast resin transformers he was...

Tips for a better Low Voltage Protection Discrimination Study

Carrying out a protection system discrimination study is critical to ensure the correct functioning of  the electrical system in the event of faults. ...

Have some knowledge to share

If you have some expert knowledge or experience, why not consider sharing this with our community.  

By writing an electrical note, you will be educating our users and at the same time promoting your expertise within the engineering community.

To get started and understand our policy, you can read our How to Write an Electrical Note